1. Field of the Invention
The present invention relates to a transmission output power control device and a transmission output power control method for use in a burst transmitter.
2. Description of the Background Art
Considering the recent increase in the number of users of cellular phone terminals, it is desirable to make as high as possible the efficiency of use of the frequency bands in the cellular phone system etc. In a burst transmitter used in the cellular phone terminal, in order to efficiently utilize the frequency band, the output power for transmission is ramped so that it rises and falls slowly, thereby preventing the spectrum from spreading in a wide range. The cellular phone system complexly uses a plurality of radio systems which use different communication systems, and the different systems use different types of modulation. Thus the cellular phone terminals include so-called dual-mode terminals which have two modulation systems.
FIG. 20 is a block diagram that shows the configuration of a dual-mode burst transmitter that uses an amplitude modulation system e.g. PDC (Personal Digital Cellular) or CDMA (Code Division Multiple Access), and a constant envelope modulation system, e.g. GSM (Global System for Mobile Communication). This configuration is now described. An I/Q signal amplitude control unit 2001 is connected via baseband signal D/A converters 2002 to a modulating unit 2003, and the modulating unit 2003 is connected to a power amplifier 2004 serving as amplifying means. The power amplifier 2004 is connected to an antenna 2005 and also to a control voltage signal selecting unit 2007 via a control voltage signal D/A converter 2006.
The I/Q signal amplitude control unit 2001 includes a waveform data generating portion 2008 and multiplication mixers 2009 connected to each other, and the waveform data generating portion 2008 includes a serial connection of a counter 2010, a table reference number generating portion 2011, and a ramp amplitude waveform data memory 2012. The modulating unit 2003 includes a quadrature modulator 2013 and a local oscillator 2014 connected to each other. The control voltage signal selecting unit 2007 includes a waveform data control function portion 2015 and a ramp amplitude waveform data memory 2016 connected thereto.
Next, its operation is described referring to FIGS. 20, 21A, and 21B. First, when a modulation system signal Sm from a base station of the radio network (for example, Sm=0 for the amplitude modulation and Sm=1 for the constant envelope modulation) selects the amplitude modulation system (Sm=0), the configuration operates as shown below. Digital baseband signals I and Q are ramped in the I/Q signal amplitude control unit 2001 and then the ramped digital baseband signals I and Q are converted to analog signals in the baseband signal D/A converters 2002. Their output amplitude waveform is shown as an analog baseband signal Ia and Qa in FIG. 21A. The ramping process performed in the I/Q signal amplitude control unit 2001 will be fully described later.
Next, in the modulating unit 2003, the ramped analog baseband signals Ia and Qa are quadrature-modulated in the quadrature modulator 2013 with a high-frequency signal outputted from the local oscillator 2014 and are thus converted to a high-frequency signal to be transmitted. The high-frequency signal outputted from the local oscillator 2014 has a frequency that is used in the amplitude modulation system selected by the base station. The high-frequency signal to be transmitted is amplified in the power amplifier 2004 and transmitted as a transmission output P from the antenna 2005. In this process, the control voltage signal selecting unit 2007 receives as its inputs the modulation system signal Sm and a transmission power level signal PCL (0, 1, . . . n) which indicates the level of the transmission power specified from the base station, and the waveform data control function portion 2015 causes digital data which corresponds to the modulation system signal Sm and the transmission power level signal PCL to be sent from the ramp amplitude waveform data memory 2016 to the control voltage signal D/A converter 2006. The control voltage signal D/A converter 2006 converts the incoming digital data to an analog signal, and during the transmission, it keeps outputting to the power amplifier 2004 a power amplifier control voltage Vc (Vc0 to Vcn) which has a predetermined constant voltage as shown in FIG. 21A. A constant voltage is thus outputted during a burst transmission section.
Now, the ramp process performed in the I/Q signal amplitude control unit 2001 is described in detail. Suppose that the modulation system signal Sm inputted to the waveform data generating portion 2008 indicates the amplitude modulation (Sm=0). Then, in the waveform data generating portion 2008, the counter 2010, configured on the basis of a clock, starts counting upon application of a transmission start pulse. As the counter 2010 is counting up, the table reference number generating portion 2011 specifies table reference numbers, n, for reading I/Q amplitude values Vpiq[n] on a table for use in ramp up. When the table reference numbers n are specified, then the I/Q amplitude values VPiq[n] corresponding to the table reference numbers n are read from the ramp amplitude waveform data memory 2012.
FIG. 22 shows, in the form of an analog signal, a ramp amplitude waveform VPiq used in the ramping process when the amplitude modulation is selected. The ramp amplitude waveform is composed of a collection of data which is required to perform the ramping process. In particular, a ramp amplitude waveform for ramping the baseband signal is represented as Viq. For the ramp amplitude waveform Viq, a ramp amplitude waveform for use in the amplitude modulation is represented as VPiq and that for use in the constant envelope modulation is represented as VGiq. When the ramping process is performed as shown in FIG. 21A, the ramp up portion exhibits such a waveform as shown in this diagram. The values VPiq[n] that form the ramp amplitude waveform VPiq are the I/Q amplitude values that correspond to the table reference numbers n; six values are set herein for the rising ramp process.
The multiplication mixers 2009 multiplies the I/Q amplitude values VPiq[n] outputted from the waveform data generating portion 2008 and the digital baseband signals I and Q to produce ramped digital baseband signals I and Q. In the amplitude modulation system, nonlinearity is not produced so much between the digital baseband signals I and Q and the transmission output P, so that the I/Q amplitude values VPiq[n] outputted from the waveform data generating portion 2008 can hold a given fixed pattern.
Next, when the constant envelope modulation is selected by the modulation system signal Sm from the radio network base station (Sm=1), the configuration operates as shown below. In the case of the constant envelope modulation, nonlinear circuitry is often used between the digital baseband signals I, Q and the transmission output P; therefore nonlinearity is produced. Accordingly the ramping process for the transmission output P is performed not in the I/Q signal amplitude control unit 2001 but in the control voltage signal selecting unit 2007 which outputs the control voltage signal Vc for controlling the power amplifier 2004. Therefore the digital baseband signals I and Q are outputted from the I/Q signal amplitude control unit 2001 without undergoing ramp process. The digital baseband signals I and Q from the I/Q signal amplitude control unit 2001 are converted to analog signals in the baseband signal D/A converters 2002 and outputted therefrom. As shown in FIG. 21B as an analog baseband signal Ia and Qa in the constant envelope modulation, the outputs exhibit an amplitude waveform having a constant amplitude that rises and falls vertically.
The analog baseband signals Ia and Qa are quadrature-modulated in the quadrature modulator 2013 in the modulating unit 2003 with the high-frequency signal from the local oscillator 2014, and are thus converted to a high-frequency signal to be transmitted. The high-frequency signal outputted from the local oscillator 2014 has a frequency that is used in the constant envelope modulation system selected by the base station. The transmission high-frequency signal outputted from the modulating unit 2003 is amplified in the power amplifier 2004 and transmitted as the transmission output P from the antenna 2005. In this process, the control voltage signal selecting unit 2007 receives as its inputs the modulation system signal Sm (Sm=1) and the transmission power level signal PCL. Then, in the control voltage signal selecting unit 2007, the waveform data control function portion 2015 reads a ramp amplitude waveform corresponding to these signals from the ramp amplitude waveform data memory 2016 and outputs the digital control voltage data for that ramp amplitude waveform to the control voltage signal D/A converter 2006 in synchronization with a transmission timing clock. On the basis of the digital data input corresponding to the transmission power level signal PCL, the control voltage signal D/A converter 2006 generates the control voltage Vc (Vc0 to Vcn) for controlling the power amplifier 2004; the control voltage Vc slowly rises and falls as shown in FIG. 21B. The control voltage signal D/A converter 2006 then outputs the control voltage Vc to the power amplifier 2004, so as to control the transmission output P into a smooth waveform so that the spectrum will not spread in a wide range.
As shown above, when the constant envelope modulation system is selected, the conventional technique realizes the ramping process by controlling the control voltage Vc to the power amplifier 2004. In this case, since the characteristics of the power amplifier 2004 differ in different radio devices, it is impossible to initially set a table for controlling the power amplifier, so that the table must be stored in a rewritable storage, i.e. in the memory 2016. Also, when the constant envelope modulation is selected, the control voltage signal Vc must be varied in accordance with the level indicated by the transmission power level signal PCL, and the ramping process must be applied to the varied version of the control voltage signal Vc. Accordingly, it is necessary to store different ramp amplitude waveforms for the control voltage Vc in correspondence with the individual levels of the transmission power level signal PCL. Therefore, a large amount of data must be stored in the ramp amplitude waveform data memory 2016 and the control voltage signal D/A converter 2006 must be controlled each time a transmission is made, which requires an increased amount of processing and increased consumption of power.
Furthermore, the ramping process must be conducted in different places depending on whether the amplitude modulation is selected or the constant envelope modulation is selected. Hence the modulation systems require their respective ramp amplitude waveform data memories and their respective operation procedures, which also requires increased consumption of power.